Background Asthma is a common chronic airway disease worldwide. Despite its large population size, China has had no comprehensive study of the national prevalence, risk factors, and management of asthma. We therefore aimed to estimate the national prevalence of asthma in a representative sample of the Chinese population. Methods A representative sample of 57 779 adults aged 20 years or older was recruited for the national cross-sectional China Pulmonary Health (CPH) study using a multi-stage stratified sampling method with parameters derived from the 2010 census. Ten Chinese provinces, representative of all socioeconomic settings, from six geographical regions were selected, and all assessments were done in local health centres. Exclusion criteria were temporary residence, inability to take a spirometry test, hospital treatment of cardiovascular conditions or tuberculosis, and pregnancy and breastfeeding. Asthma was determined on the basis of a self-reported history of diagnosis by a physician or by wheezing symptoms in the preceding 12 months. All participants were assessed with a standard asthma questionnaire and were classed as having or not having airflow limitation through pulmonary function tests before and after the use of a bronchodilator (400 mu g of salbutamol). Risk factors for asthma were examined by multivariable-adjusted analyses done in all participants for whom data on the variables of interest were available. Disease management was assessed by the self-reported history of physician diagnosis, treatments, and hospital visits in people with asthma. Findings Between June 22, 2012, and May 25, 2015, 57 779 participants were recruited into the CPH study. 50 991 (21 446 men and 29 545 women) completed the questionnaire survey and had reliable post-bronchodilator pulmonary function test results and were thus included in the final analysis. The overall prevalence of asthma in our sample was 4.2% (95% CI 3.1-5.6), representing 45.7 million Chinese adults. The prevalence of asthma with airflow limitation was 1.1% (0.9-1.4), representing 13.1 million adults. Cigarette smoking (odds ratio [OR] 1.89, 95% CI 1.26-2.84; p=0.004), allergic rhinitis (3.06, 2.26-4.15; p<0.0001), childhood pneumonia or bronchitis (2.43, 1.44-4.10; p=0.002), parental history of respiratory disease (1.44, 1.02-2.04; p=0.040), and low education attainment (p=0.045) were associated with prevalent asthma. In 2032 people with asthma, only 28.8% (95% CI 19.7-40.0) reported ever being diagnosed by a physician, 23.4% (13.9-36.6) had a previous pulmonary function test, and 5.6% (3.1-9.9) had been treated with inhaled corticosteroids. Furthermore, 15.5% (11.4-20.8) people with asthma reported at least one emergency room visit and 7.2% (4.9-10.5) at least one hospital admission due to exacerbation of respiratory symptoms within the preceding year. Interpretation Asthma is prevalent but largely undiagnosed and undertreated in China. It is crucial to increase the awareness of asthma and disseminate standardised treatment in clinical settings to reduce the disease burden. Copyright (C) 2019 Elsevier Ltd. All rights reserved.